1. Field of the Invention
The present invention relates to a method of the preparation of ultrafine particles of water-insoluble or hardly water soluble organic compounds and stable water dispersion thereof.
2. Description of the Prior Art
When various kinds of materials such as metals, ceramics are pulverized into fine particles (or powder), it is observed that many discrete planes are formed and the interface (or more precisely specific surface) of the material is substantially increased. Moreover, many defects are formed in the crystalline structure thereof and are chemically activated, because of their small diameter. As a result, these materials in the form of fine particles exhibit a lot of interesting properties such as high adsorptivity, high hygroscopicity, as well as catalytic activity. Thus, processes, in which powder materials are used, are frequently applied in many field such as chemical industries, medicines, insecticide or pesticide, foods, refinery, ceramics or the like.
These powder may be prepared according to various kinds of methods, for example, evaporation-condensation process, sputtering process, vapour deposition technique such as thermal decomposition or photolysis of metal halides or organometallic compounds, precipitation reaction in an aqueous solution, electrolytic process, hydronic discharge technique, spray drying method as well as mechanical pulverization and grain boundary corrosion technique or the like.
While, so-called ultrafine particles having a diameter of an order of approximately microns or angstroms have drawn attention in particular in the field of inorganic materials. The ultrafine particles of inorganic materials present excellent physical and chemical properties and are expected to apply as magnetic materials, material for powder metallurgy, chemical catalyst, light or electromagnetic wave absorber, semiconductor materials. Under these circumstances, various methods for manufacturing such ultrafine powder have been proposed and put into practical use. An example of such method comprises evaporating a material in a rare gas atmosphere while heating and condensing the resulting vapour of the material in the rare gas atmosphere to form ultrafine particles (this method is referred to as evaporation in gas atmosphere technique). Other methods, in which electric resistance element, plasma jet, induction infrared laser or plasma arc discharge is used, are also known in the art.